Pierson syndrome with numerous dilated tubules masquerading as autosomal recessive polycystic kidney disease: a case report.

Pierson syndrome, characterized by congenital nephrotic syndrome, ocular abnormalities, and neurological defects, is caused by biallelic pathogenic variants in LAMB2. LAMB2 encodes laminin β2, a key component of basement membranes that is predominantly expressed in the glomeruli, eyes, and neuromuscular junctions. The renal histopathology of Pierson syndrome typically shows diffuse mesangial sclerosis (DMS), with occasional tubulointerstitial atrophy and fibrosis. We report a case of Pierson syndrome characterized by DMS and prominent tubular dilatation. A fetal ultrasound at 23 weeks of gestation revealed hyperechoic kidneys, which gradually enlarged, accompanied by the onset of anhydramnios from 31 weeks. The patient was delivered at 39 weeks of gestation, weighing 3,132 g, without placentomegaly. Postnatal respiratory failure due to pulmonary hypoplasia required extracorporeal membrane oxygenation, and hemodialysis was initiated for anuria. Left nephrectomy was performed on day 8 of life, revealing replacement of the renal parenchyma by numerous irregularly dilated tubules with eosinophilic casts. The right kidney reached maximal enlargement by 1 month of age and subsequently began to shrink. Ocular findings included bilateral microcoria and cataracts. Whole-exome sequencing identified compound heterozygous truncating variants in LAMB2 (p.Gln1507Ter and p.Gln1622Ter). This case highlights the need to consider Pierson syndrome in the differential diagnosis of prenatally detected hyperechoic and enlarged kidneys, in addition to polycystic kidney disease.